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891.
北京城郊山地森林游憩机会谱构建 总被引:6,自引:0,他引:6
20世纪中叶,到森林中休闲游憩的人数剧增,为了保护生态环境,同时为游客提供高质量的游憩体验,美国林务局的管理者和专家发展了游憩机会谱(ROS)理念和管理框架,其主要以游憩需求为导向,依据"自然环境"、"社会环境"和"管理环境"指标对游憩区进行分类分级,编制游憩机会清单,对资源进行清查、规划和管理。本文在介绍ROS理论的基础上,结合北京市民森林游憩的需求特征和森林游憩区当前的管理体制和开发利用现状,筛选出"自然程度"、"偏远程度"、"游客密度"和"管理强度"4个评价指标,分析提出了北京山地森林游憩机会谱,将北京城郊山地森林游憩区分为城郊开发区域、城郊自然区域、乡村开发区域、乡村自然区域和半原始区域五个游憩机会等级,并结合目前的北京市游憩资源的利用和管理现状,用GIS作图直观展示了各游憩机会的分布,分析比较了各游憩机会的供需状况,为北京城郊森林游憩的规划和管理提出了合理化建议。 相似文献
892.
893.
Analysis of characteristics of time-frequency correlations between runoff, tidal range and salinity in the Changjiang Estuary 总被引:2,自引:0,他引:2
Power spectrum and cross-wavelet transform analysis was adopted to study the time-frequency characteristics and multiscale correlations between runoff, tidal range and salinity in the Changjiang Estuary based on the runoff data collected at the Datong Station, the tidal range measured at the Baozhen Station, and the salinity at the Baogang Station from 2008 to 2009. The variations of the salinity showed significant periodicity at scales of 2-3, 7-8, 14-15 and 26-30 d. The correlation between the salinity and the runoff and the tidal range were found to be significantly related to shock at scales of 5-7, 14-15, 26-30 d and 0.5 a. The correlation between the runoff and the salinity was mainly in the same phase, while the correlation between the tidal range and the salinity was in the antiphase. Different frequency bands were related to different degrees, and their relevance increased as the resonance frequency decreased. In addition, changes of the seasonal runoff were obvious. Specifically, a point of discontinuity was reached in early June with a cycle of 7-8 d, which coincided with the periodicity of plum rains in the Changjiang-Huaihe region. High-frequency changes (8-16 d period) of the salinity corresponded to the time domain in January-April 2008, February-April 2009 and October-December 2009 and exhibited an approximately 0.5 a (184 d) long frequency oscillation. Short-period changes were found to be stronger than long-period changes. Cross-wavelet transforms for the salinity, the runoff and the tidal range revealed local features in the time domain, while the significant levels of different periodic oscillations were observed in the frequency domain. The correlation characteristics of the salinity and the runoff were significant in the 80-90 d frequency domain, indicating that the major impact of the runoff on the salinity was reflected in seasonal changes. The tidal range on the small scale of 14-15 and 30-32 d was more obvious than the runoff. 相似文献
894.
895.
基于广义逆和奇异值分解理论,研究核磁共振T2谱反演的截断法和阻尼法。首先给出反演问题的M-P广义逆解;然后对系数矩阵进行奇异值分解求其M-P广义逆,对奇异值进行截断或者加阻尼,保证解的稳定性兼顾其分辨率;最后利用迭代技术实现解的非负约束。数值仿真实验和岩心T2谱反演表明:对于双峰谱,在信噪比SNR≥10时,截断法和阻尼法反演T2谱的分辨率和稳定性都很高;截断法截断因子选择范围小,在SNR<10时解的分辨率和稳定性差;阻尼法阻尼因子选择范围大,在SNR<10时解的稳定性好,但短组分分辨率低,长组分分辨率高。对于三峰谱,当SNR≥20时,截断法和阻尼法反演的T2谱光滑连续,具有三峰结构;当SNR<20时两者均不能反演出与构造谱接近的三峰谱。因此,2种方法可应用于SNR≥10的双峰谱和SNR≥20的三峰谱反演;从分辨率和稳定性、平滑噪声及截断和阻尼因子的选取上,阻尼法略优于截断法。 相似文献
896.
897.
David C. Mosher 《Marine and Petroleum Geology》2011,28(8):1540-1553
It is the intent of this paper to explore a significant extent of an entire passive continental margin for hydrate occurrence to understand hydrate modes of occurrence, preferred geologic settings and estimate potential volumes of methane. The presence of gas hydrates offshore of eastern Canada has long been inferred from estimated stability zone calculations, but little physical evidence has been offered. An extensive set of 2-D and 3-D, single and multi-channel seismic reflection data comprising in excess of 140,000 line-km was analyzed. Bottom simulating reflections (BSR) were unequivocally identified at seven sites, ranging between 250 and 445 m below the seafloor and in water depths of 620-2850 m. The combined area of the BSRs is 9311 km2, which comprises a small proportion of the entire theoretical stability zone along the Canadian Atlantic margin (∼715,165 km2). The BSR within at least six of these sites lies in a sedimentary drift deposit or sediment wave field, indicating the likelihood of grain sorting and potential porosity and permeability (reservoir) development. Although there are a variety of conditions required to generate and recognize a BSR, one might assume that these sites offer the most potential for highest hydrate concentration and exploitation. Total hydrate in formation at the sites of recognized BSR’s is estimated at 17 to 190 × 109 m3 or 0.28 to 3.12 × 1013 m3 of methane gas at STP. Although it has been shown that hydrate can exist without a BSR, the results from this regional study argue that conservative estimates of the global reserve of hydrate along continental margins are necessary. 相似文献
898.
A virtual wave gauge (VWG) technique based on stereo imaging is developed to remotely measure water wave height, period, and direction. VWG minimizes computational costs by directly tracking the elevation of the water surface at selected points of interest using a Eulerian based dynamic searching algorithm. Results show that the VWG technique developed in this paper dramatically improves efficiency by two orders of magnitude compared to the traditional Lagrangian–Eulerian based point cloud method of stereo image processing. VWG is tested against traditional wave wire gauges to within 98% accuracy for significant wave height. Furthermore, the flexibility of the VWG is demonstrated in two field applications. First in an offshore breaking wave case, an array of VWGs is used to efficiently measure wave directionality. Second to investigate the reflection coefficient of a rock-mounted structure interacting with nearshore waves, linear and spatial VWG arrays are designed and implemented based on a priori information of the wave field from a preliminary VWG measurement. Overall, we demonstrate that the flexible and computational efficient VWG technique has the potential to make real-time remote stereo imaging wave measurements a reality. 相似文献
899.
The friction coefficient in the permeability parameter of a perforated wall has been estimated on the basis of a best fit between measured and predicted values of such hydrodynamic coefficients as reflection and transmission coefficients. In the present study, an empirical formula for the friction coefficient is proposed in terms of known variables, i.e., the porosity and thickness of the perforated wall and the water depth. This enables direct estimation of the friction coefficient without invoking a best fit procedure. To obtain the empirical formula, hydraulic experiments are carried out, the results of which are used along with other researchers' results. The proposed formula is used to predict the reflection and transmission coefficients of various types of structures including a perforated wall. The concurrence between the experimental data and calculated results is good, verifying the appropriateness of the proposed formula. It is also shown that the proposed formula can be used for irregular waves as well. 相似文献
900.
Experimental researches on reflective and transmitting performances of quarter circular breakwater under regular and irregular waves 总被引:1,自引:1,他引:0
A series of regular and irregular wave experiments are conducted to study the reflective and transmitting performances of quarter circular breakwater (QCB) in comparison with those of semi-circular breakwater (SCB). Based on regular wave tests, the reflection and transmission characteristics of QCB are analyzed and a few influencing factors are investigated. Then, the wave energy dissipation as wave passing over the breakwater is discussed based on the hydraulic coefficients of QCB and SCB. In irregular wave experiments, the reflection coefficients of QCB and their spectrums are studied. Finally, the comparisons between the experimental results and numerical simulations for QCB under regular and irregular wave conditions are presented. 相似文献